linux-kernel - Re: [PATCH v4 1/2] vTPM: support little endian guests

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Message-Id: <201507162043.52754.PeterHuewe@gmx.de>
Date:	Thu, 16 Jul 2015 20:43:52 +0200
From:	Peter Hüwe <PeterHuewe@....de>
To:	"Hon Ching(Vicky) Lo" <honclo@...ux.vnet.ibm.com>
Cc:	tpmdd-devel@...ts.sourceforge.net,
	Ashley Lai <ashley@...leylai.com>,
	Vicky Lo <honclo2014@...il.com>, linux-kernel@...r.kernel.org,
	Joy Latten <jmlatten@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 1/2] vTPM: support little endian guests

Hi Vicky,
Am Donnerstag, 16. Juli 2015, 19:54:15 schrieb Hon Ching(Vicky) Lo:
> Hi Peter,
> 
> On Mon, 2015-07-13 at 23:08 +0200, Peter Hüwe wrote:
> > Hi Vicky,
> > 
> > sorry for the late reply
> > 
> > > This patch makes the code endianness independent. We defined a
> > > macro do_endian_conversion to apply endianness to raw integers
> > > in the event entries so that they will be displayed properly.
> > > tpm_binary_bios_measurements_show() is modified for the display.
> > > 
> > > Signed-off-by: Hon Ching(Vicky) Lo <honclo@...ux.vnet.ibm.com>
> > > Signed-off-by: Joy Latten <jmlatten@...ux.vnet.ibm.com>
> > > 
> > > b/drivers/char/tpm/tpm_eventlog.h index e7da086..267bfbd 100644
> > > --- a/drivers/char/tpm/tpm_eventlog.h
> > > +++ b/drivers/char/tpm/tpm_eventlog.h
> > > @@ -6,6 +6,12 @@
> > > 
> > >  #define MAX_TEXT_EVENT		1000	/* Max event string length */
> > >  #define ACPI_TCPA_SIG		"TCPA"	/* 0x41504354 /'TCPA' */
> > > 
> > > +#ifdef CONFIG_PPC64
> > > +#define do_endian_conversion(x) be32_to_cpu(x)
> > > +#else
> > > +#define do_endian_conversion(x) x
> > > +#endif
> > 
> > Why is this macro needed?
> > shouldn't the be32_to_cpu macro already do correct thing?
> > Or am I missing something here?
> > 
> > 
> > Thanks,
> > Peter
> 
> The macro is defined to not do the conversion in the architecture
> that does not need it.

Unfortunately I'm still not convinced this is needed?
 be32_to_cpu(x)
should already do the right thing if no conversion is needed ? (being defined 
as (x)) 
Or is it not?



Peter
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